ISTANBUL - Turkey's government derided a high-profile prosecutor behind a damaging corruption investigation as a showman on Thursday, after he accused Prime Minister Tayyip Erdogan of threatening him and telling him to halt the inquiry.

An opinion poll, the first since the corruption scandal broke last month, showed Erdogan's AK Party losing some support, but still well ahead of any rivals.

Former deputy chief Istanbul prosecutor Zekeriya Oz, who was reassigned earlier this week as part of a government crackdown on judiciary and police, said his police protection vehicle, provided when he faced death threats during a coup plot investigation, had been removed without explanation.

"Those who carried out this unlawful action will be responsible for anything that happens to me personally or my family," he said in a statement.

Oz said he had been warned by two senior members of the judiciary to stop the corruption investigation, which has gripped Turkey for weeks and poses the biggest threat yet to Erdogan's 11-year rule.

"(They) told me the prime minister was angry at me ... They said the investigations against the government should be halted immediately or I would suffer harm," Oz said.

"I said to them the worst thing that could happen to me would be death and that, if I died, I would be a martyr in the line of duty and this would be an honour for me."

Erdogan's aides denied the prime minister had sent anyone to speak to Oz, describing his comments as lies.